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Web Content Accessibility Guidelines (WCAG) 2.0

In order to understand accessibility requirements for PDF it is useful to take a look at accessibility requirements for the Web. The W3C published its »Web Content Accessibility Guidelines« WCAG 2.0 in 2008 (also standardized as ISO/IEC 40500:2012). It contains twelve general accessibility guidelines which are organized according to the following principles:

Content should be perceivable, e.g. alternate text should be available for images and other nontextual content.

Content should be operable, e.g. all functionality should be available from a keyboard.

Content should be understandable, e.g. all text should be readable.

Content should be robust for compatibility with current and future tools.

These guidelines describe a total of 61 success criteria which must be met to make content accessible. The success criteria are grouped in three conformance levels, ranging from A (minimum conformance) to the medium level AA and up to the highest level AAA. In order to achieve minimum accessibility requirements only Level A criteria must be met.

Applying WCAG to PDF

WCAG is a technology-independent standard: it is not targeted at a specific technology such as HTML or server-side scripting, but describes accessibility requirements in a very general manner. An advisory (i.e. non-normative) document called »Techniques for WCAG 2.0« discusses general techniques for achieving WCAG conformance and provides techniques for specific technologies such as HTML, CSS, Flash and PDF. The advisory »PDF Techniques for WCAG 2.0« applies WCAG requirements to PDF and provides useful examples which demonstrate in detail how a particular accessibility requirement can be met. The examples are targeted at users of Acrobat, content creation software (e.g. Microsoft Word, OpenOffice) and PDF developers.

For the convenience of PDFlib users the document »PDFlib Techniques for WCAG 2.0« (available in the PDFlib documentation) explains procedures which can be used to meet WCAG requirements when creating accessible documents with PDFlib.

WCAG and PDF/UA

While the W3C’s PDF techniques are useful, they do not cover all technical PDF details for achieving full accessibility. The PDF/UA standard clarifies and simplifies PDF requirements to meet WCAG 2.0. While PDF/UA conformance ensures WCAG conformance for native PDF page content, there are some areas where WCAG imposes additional requirements. In particular, WCAG requirements must be met in addition to PDF/UA for embedded multimedia content and scripting in order to make such content types in PDF accessible.

The relationship of WCAG and PDF/UA rules is explained in detail in a document published by AIIM. »Achieving WCAG 2.0 with PDF/UA« contains a reference table which maps WCAG success criteria to the corresponding PDF/UA requirements.

There are only two topics where PDF/UA imposes additional requirements beyond WCAG: in order to improve document navigation PDF/UA mandates various nesting rules for heading tags, while WCAG isn’t concerned about nesting of headings. PDF article threads must be applied appropriately; however, this PDF feature is somewhat outdated and rarely used in newly created PDF documents.

Note that a PDF document may conform to WCAG 2.0 without conforming to PDF/UA, but achieving WCAG conformance is much simpler with PDF/UA than without.